1. Field of the Invention
The present invention is directed toward an apparatus and method for determining localized strain in a target body by identifying sets of features in reflected echo sequences and by comparing sets of features to determine time shift values between features.
2. Discussion of the Prior Art
Prior art techniques for making elastographic measurements require a large amount of data transfer and large processing times in order to obtain good elastographic images, thereby hindering the use of high quality real time elastography. This also hinders the use of hand held elastographic imaging systems.
Prior art elastographic data processing techniques utilize all information in the reflected signal. Much of this information is redundant and is therefore not useful for imaging purposes. The present invention offers the advantage of acquiring only useful and non-redundant features in the reflected signal, thereby reducing data acquisition time and processing time, without compromising the quality of the elastogram.
Prior art elastographic data processing techniques also utilize correlation schemes which rely upon uniform shifts between signals. Elastography signals inherently have non-uniform shifts. Accommodating for such non-uniform shifts requires apriori knowledge, which is difficult to acquire in practical situations, such as in-vivo tests. The present invention does not require any apriori information and it adaptively accounts for non-uniform shifts.
Many prior art methods stretch the post-compression A-lines to accommodate for non-uniform shifts. The present invention does not require such post-compression stretching.
Other prior art elastographic methods employ time domain correlation techniques. Stretching is essential to obtain high quality elastograms using such correlation techniques. In many practical situations, such as breast or prostate imaging, an accurate estimate of the compressed distance, and hence the stretch factor, is not readily ascertainable for all A-lines in a transducer array. This results in using local adaptive stretching of the post-compression A-line. Such post-adaptive stretching techniques are significantly slower than global stretching algorithms used for analyzing elastographic data.
Other prior art elastographic techniques employ spectral analysis that does not comprise stretching. Such techniques are suitable only for strains of more than five percent and have significantly lower signal to noise ratios (SNR) than conventional techniques, such as time domain correlation. An advantage of the present invention over spectral techniques is that it provides real time processing of up to 30 frames per second for a target depth of 60 millimeters in a software implementation. The present invention may be implemented in a hardware device, further increasing the imaging speed and thereby resulting in feasibility for use in displaying a simultaneous sonogram and elastogram. The present invention further offers the advantage of being able to switch between temporal tracking and cumulative averaging, without adversely affecting processing time. The present invention allows a multi-resolution elastogram without any increase in processing time. Prior art, elastographic methods require increased processing time in order to produce a multi-resolution elastogram.
The present invention is directed toward a method for determining localized strain in a target body. This method comprises the steps of acoustically coupling at least one ultrasound source to a target body and then emitting a first pulse of ultrasound energy of a known central wavelength from the source along the first radiation access into the target body. The method embodiment of the invention further comprises recording a first echo sequence having at least one echo segment arriving in response to the first pulse of ultrasound energy and then locating at least one feature in the first echo sequence arriving in response to the first pulse of ultrasound energy as a function of time to form a first set of features. The term xe2x80x9cfeature,xe2x80x9d as used herein, refers to any discernable echo segment characteristic or combination of characteristics. Features may include, but are not limited to, level crossings, peaks, valleys, or combinations thereof. The term xe2x80x9czero crossing,xe2x80x9d as used herein, refers to a level crossing that occurs at a designated zero value on the Y axis.
The method of the present invention further comprises displacing the target body along the first radiation axis by a known displacement and emitting a second pulse of ultrasound energy from the source along the first radiation axis into the target body.
The method embodiment of the invention further comprises recording a first echo sequence having at least one echo segment arriving in response to the second pulse of ultrasound energy and then locating at least one feature in the first echo sequence arising in response to the second pulse of ultrasound energy as a function of time to form a second set of features.
The first set of features is then compared to the second set of features to determine a set of time shift values as a function of time. Based upon this comparison, the local strain in the target body along portions of the first radiation access are determined.
The present invention is also directed toward an apparatus for determining localized strain in a target body. The apparatus comprises a transducer capable of receiving a reflected ultrasound echo sequence comprising at least one echo segment from a target body. The transducer is further capable of outputting an electrical analog signal indicative of the echo sequence. The apparatus embodiment further comprises a pulser electrically coupled to the transducer and a clock electrically coupled to trigger the pulser in order to send electrical energy to the transducer.
The apparatus embodiment further comprises a filter coupled to receive the electrical analog signal from the transducer. The filter is capable of producing a filtered analog electrical signal from the incoming signal.
The invention further comprises a feature detector coupled to receive a filtered electrical analog signal from the filter. The feature detector is capable of detecting preselected features in the filtered electrical analog signal as a function of time, as measured by the clock. The featured detector is further capable of outputting a feature attribute signal indicative of the magnitude and temporal location of each feature.
The apparatus embodiment of the present invention further comprises a buffer coupled to the feature detector and capable of receiving and storing the feature attribute signal. The invention further comprises a counter coupled to the buffer and capable of counting the number of features stored in the buffer.